The present invention relates to a power converting apparatus of, for example, inverters for DC-AC conversion and converters for AC-DC conversion of a single phase and multiphases, inverters for AC-DC-AC conversion to drive a multiphase AC motor, active filters, and the like and, more particularly, to a power converting apparatus in which a light triggered and light quenched electrostatic induction thyristor is used as a switching element, and a light trigger pulse and a light quench pulse are supplied to the thyristor at a timing corresponding to the pulse width modulation, whereby a predetermined power converting operation is performed.
As is well known, for example, in the power converting apparatus of the DC-AC converting inverter, AC-DC converter, or the like, a reverse-blocking three-terminal thyristor (SCR), a light triggered thyristor, or the like is used as a switching element. A three-phase AC bridge circuit is widely used as a general circuit constitution. Such a thyristor is the commutation turn-off type element. By performing the turn-on and commutation turn-off at a frequency of, e.g., about 50 to 60 Hz by use of the commutation cycle, this thyristor can execute the DC-AC conversion and AC-DC conversion.
On the other hand, for example, in the power converting apparatus which handles a large electric power, such as applied to the DC power transmission, a plurality of light triggered thyristors are connected in series-parallel, thereby allowing the switching operations of the light-triggered turn-on and commutation turn-off to be executed at a frequency of 50 to 60 Hz.
However, the power converting apparatus using the three-phase AC bridge circuit using such a commutation turn-off type thyristor has the following problems. The AC frequency which can be handled is as low as 50 to 60 Hz. It takes a long time, e.g., hundreds of .mu.sec, to perform the commutation turn-off of the light triggered thyristor. Therefore, this apparatus is unfitted for the high speed operation.
Therefore, a power semiconductor device of the self-turn-off type also has conventionally been used as a switching device for use in the above-mentioned power converting apparatus. As the self-turn-off type power semiconductor device, for example, various kinds of transistors of power bipolar transistor, power MOS (Metal Oxide Semiconductor) field effect transistor (FET), power electrostatic induction transistor (SIT), and the like, and a gate turn-off thyristor (GTO) are used.
The self-turn-off type semiconductor devices such as the above transistors, gate turn-off thyristor, and the like can perform the switching operations as their gates are electrically controlling the gate (or base). Also, the time required for turn-off is so short to be a few to tens of .mu.sec. Therefore, by constituting a single-phase or multiphase inverter or converter in a manner such that the self-turn-off type semiconductor device executes the switching operations by use of, e.g., a control system due to a pulse width modulation, such a device can advantageously realize the high-speed operation.
In the power converting apparatus using such a self-turn-off type semiconductor device, however, a control circuit must be provided to control the semiconductor device since the gate (or base) needs to be electrically controlled. The apparatus is inevitably complicated. In the gate turn-off thyristor, control circuits are necessary for both of the turn-on and turn-off, respectively. This will also likely complicate the constitution. Moreover, in the case of handling a large electric power, a plurality of semiconductor elements are connected in series-parallel, and more circuit elements are required to further complicate the structure. Moreover, since it is difficult to electrically isolate the portion which handles a large electric power from the control circuit portion, the magnitude of the electric power which can be handled is also limited.